Supercritical mixtures of high purity CO2 and organic co-solvents, such as ethanol, are used in the production of semiconductor wafers. This includes post-etch cleaning, residue removal, and metal and dielectric deposition. For a commercial process, CO2 flows are large and CO2 needs to be recycled after each wafer production step. CO2 recycle for semiconductor requirements can only be done if the co-solvents and dissolved impurities can be substantially removed from the recycle stream.
For a large-scale chemical production system, the amounts of CO2/co-solvent waste generated are significant. To make the process more economical, CO2 can be recycled, as long as the co-solvent (and other impurities) can be separated from the CO2. To accomplish this, the prior art discloses the use of distillation columns, where the CO2 and the co-solvents are separated. This system will work as long as there are only two major components in the system, namely CO2 and the co-solvent. If trace amounts of other components are present, this process has to be substantially altered with additional equipment, design changes and added expense. Still, the separation of all measurable traces is not always possible with known systems.
Previous processes for recovery of carbon dioxide for reuse in industrial processes such as semiconductor wafer manufacturing require the use of accessory equipment such as boilers and condensers for distilling and condensing the solvent waste stream, together with significant energy requirements.
U.S. Pat. No. 4,349,415 discloses a process for separating organic liquid solutes from their solvent mixtures, wherein the extractant can be carbon dioxide used in the supercritical state.